The present invention relates generally to data storage communication channels. More particularly, the present invention relates to a disc or tape drive communication channel in which data is frequency multiplexed over a common transmission medium.
A typical disc drive includes one or more discs, a transducer, a head-gimbal assembly supported above each disc, and a drive controller. The drive controller controls the disc drive to store information on and retrieve information from the disc based on commands received from a host system or disc drive initiator. Information is stored on a magnetic disc, for example, by providing a write signal to the transducer to encode flux reversals on the surface of the magnetic disc. The flux reversals represent the data to be stored. In retrieving data from a magnetic disc, the transducer senses the flux reversals and generates a read signal based on the flux reversals. The read signal is then decoded by the drive controller.
Data is typically transmitted between the disc drive and a host system or disc drive initiator over a communication channel, such as a serial Fiber Channel (FC) a Fiber Channel Arbitrated Loop (FC-AL) or a parallel Small Computer System Interface (SCSI) channel. The effective data transfer rate between the disc drive and the host system or disc drive initiator is therefore limited by the data transfer rate through the communication channel. Faster data rates have been achieved in communication channels by increasing the clocking rate and by changing the encoding/decoding scheme to one that is more efficient. However, these performance improvements are limited to the available transceiver and encoding technology. Other solutions which provide economical performance improvements with existing technology are desired.
Fast data transfer rates are particularly important in disc drive arrays. A disc drive array includes a plurality of disc drives which are coupled to an array controller through a communication channel. The array controller controls operation of the disc drive array so that, should one disc drive fail, the information stored on that disc drive can be recovered using information stored on the remaining disc drives in the disc drive array. Because the information stored in a disc drive array is often much more valuable than the disc drives themselves, disc drive arrays are often referred to as Redundant Arrays of Inexpensive Discs (RAID).
The present invention addresses these and other problems, and offers other advantages over the prior art, particularly for disc drive arrays.
The present invention relates to a data storage communication channel which increases the effective data transfer rate to a plurality of individual data storage devices over a transmission medium.
In accordance with one embodiment of the invention, the data storage communication channel includes a transmission medium, an initiator interface and a frequency selective multiplexer. The transmission medium includes a transmission path. The initiator interface includes first and second serial transmit ports for transmitting first and second serial transmit signals, respectively. The frequency selective multiplexer includes first and second modulators which are operatively coupled to the first and second serial transmit ports, respectively. The first and second modulators modulate the first and second serial transmit signals in first and second frequency bands, respectively, wherein the first frequency band is separate from the second frequency band. A circulator is operatively coupled between the first and second modulators and the transmission path. The circulator combines the first and second modulated serial transmit signals into a transmission signal and applies the transmission signal to the transmission path.
Another aspect of the present invention relates to a data storage communication channel including a transmission medium, a frequency selective demultiplexer and first and second data storage interfaces. The transmission medium includes a transmission path for carrying a transmission signal having first and second serial, digital transmit signals modulated in first and second frequency bands, respectively. The frequency selective demultiplexer includes first and second demodulators which are operatively coupled to the transmission path to receive the transmission signal. The first and second demodulators demodulate the first and second serial, digital transmit signals from the transmission signal in the first and second frequency bands, respectively. The first and second data storage interfaces are operatively coupled to the first and second demodulators, respectively, to receive the demodulated first and second serial transmit signals.
Another aspect of the present invention relates to a method of transmitting a plurality of data signals from a data storage initiator interface to a plurality of data storage interfaces which are operatively coupled to a data storage system backplane. The method includes the steps of: (a) frequency multiplexing the plurality of data signals together, wherein each of the plurality of data signals is modulated in a respective frequency band and wherein the respective frequency bands are separate from one another; (b) transmitting the frequency multiplexed plurality of data signals to the data storage system backplane through a serial transmission medium; (c) frequency demultiplexing the frequency multiplexed plurality of data signals received at the data storage system backplane, wherein each of the plurality of data signals is demodulated from the respective frequency band; and (d) applying each of the frequency demultiplexed plurality of data signals to a respective one of the plurality of data storage interfaces.